Letter 27037

Coating for aluminum heat sink [Massachusetts] 

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I have an aluminum heat sink used in a cleanroom environment and therefore the surface needs to sealed to prevent oxidiation and contamination to sensitive materials. Will a chromate coating have sufficient thermal conductivity to ensure good heat transfer? And is chromate a sacrificial coating or will it resisit oxidation even if scratched? If the answer to these questions is 'no' than what would be the best coating to use?

Jim Sbrogna
Semiconductor Equipment Engineer - Natick , MA, USA

Ideally, heat sinks should be anodized. Chromate coatings will not cause thermal conductivity problems, but they are electrically conductive, which could be a problem. Chromate is not a sacrificial coating but it is "self healing" so it is helpful even in an environment where scratching is possible.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

In addition to all the accurate advice Ted sent to you, you may need also to know that bare unpainted chromate conversion coatings are limited to a surface temperature of 140 F, above which the coatings disintegrate. Absolutely not suitable for a very hot sink.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

The coating of choice for heat sinks has been electroless nickel forever. Corrosion resistant, conductive, both thermal and electrical. Even looks good.

Dan Weaver Team Metal Finishing - Toccoa, GA

Anodizing should be fine. Aluminum oxide is tough, proven, and is thermally a good conductor due to lattice phonon effects.

Dale Woika
- Bellefonte, PA, USA

Electroless nickel is the best coating if you want maximum heat transfer. Anodize coatings are dielectric and have poor heat transfer characteristics. They are very corrosion resistant as is electroless nickel.

Don Baudrand Don Baudrand, Consultant   Poulsbo, WA. USA

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